Joanna: What are you doing?
Chandler: I'm getting dressed.
Chandler: Because when I go outside naked, people throw garbage at me.
When Rachel finds out that Ross and Julie are getting a cat, watch Rachel's neck. When she says "together?" she's not wearing a necklace; cut to Ross and Julie for a fraction of a second, then when it cuts back to Rachel saying "both of you?" she's suddenly wearing a necklace. It then disappears again when she says "isn't that just lovely?" hanging off the side of the tray she's holding.
Matthew Perry's wit is so legendary that the scriptwriters have often incorporated his gags into the show.